1990 740: Check engine light but no fault codes

[BoKu]

My new (to me) 1990 744 with LH 2.4 is showing the Check Engine light. But when I pull the codes, I get the 1-1-1 "no faults" code for both FI (socket 2) and ignition (socket 6).

Is there any other fault that would show the Check Engine light without logging a fault code? Or should I pursue my suspicion that the fault lies with the circuitry that tests the Check Engine light itself?

My recollection of such things is that the test mode grounds the light through diodes to the little red alternator wire, and there does seem to be some funkiness in that circuit.

Any advice appreciated.

Thanks, and best regards to all

Bob "BoKu" K.
http://www.hpaircraft.com